The uncatalysed and copper(II) promoted hydrolysis of 4-nitrophenyl glycinate

Abstract

The uncatalysed hydrolysis of 4-nitrophenyl glycinate has been studied over a range of pH at I= 0.1 mol dm^–3(KNO₃) and 35 °C. The ionization equilibrium of 4-nitrophenyl glycinate can be represented as in (i) where the pK is ca. 7.1 at 25 °C. Rate constants have been obtained for both NH₃CH₂[graphic omitted]H₄NO₂-4 [graphic omitted] NH₂C[graphic omitted]CO₂C₆H₄NO₂-4 + H⁺(i) water and base hydrolysis of the species L and HL⁺. For the species L, k_OH= 2.3 × 10² dm³ mol^–1 s^–1 and k_H2O= 6.1 × 10^–5 dm³ mol^–1 s^–1 while for HL⁺, k_OH= 3.8 × 10⁵ dm³ mol^–1 s^–1 and k_H2O= 2.3 × 10^–6 dm³ mol^–1 s^–1 at 35 °C. The hydrolysis of the ester is strongly promoted by copper(II), and under the experimental conditions employed, it has been shown that the metal-ion promotion involves the steps (ii) and (iii) with K_M= 2.7 × 10² dm³ mol^–1 and k_OH= 6.6 × 10⁶ Cu²⁺+ L[graphic omitted][CuL]²⁺(ii), [CuL]^2–+ OH^– [graphic omitted] Products (iii) dm³ mol^–1 s^–1 at 35 °C. Base hydrolysis of [CuL]²⁺ is ca. 3 × 10⁴ times faster than for L and some 18 times faster than for HL⁺ at 35 °C. Possible mechanisms for these reactions are considered.